A 22-year-old woman presented with palpitations, agitation, heat intolerance and unintentional weight loss that had started several months before. Pharmacotherapy for hyperthyroidism was prescribed, but a year later thyroidectomy was performed in connection with a lack of treatment compliance. A few hours after the operation the patient developed a tingling sensation and muscle cramp, which were found to be due to severe hypocalcaemia. Although surgery was complicated by hypoparathyroidism, there was an unusually high need for calcium combined with a low calcium excretion in the urine. Such a high need for calcium due to the increased bone reconstruction induced by the hyperthyroidism is referred to as the hungry bone syndrome. One should be particularly alert to this complication in cases of severe, prolonged hyperthyroidism, certainly in the presence of existing or peroperatively induced damage to the parathyroids. In this patient, calcium suppletion led to normalisation of the serum calcium level two weeks postoperatively; she was discharged from the hospital in good condition after 3 weeks.